Balance of Terror is a key Star Trek building block. The previous episodes have tended to concentrate on civilisations either long dead or dying. But today for the first time we encounter a race – the Romulans – who are a similar size to the Federation and also have an interest in space exploration.

Mind you, at this point the Federation has yet to be formally introduced (that wouldn’t occur until A Taste of Armageddon). But what Balance of Terror does so well is to dig into the Earth/Romulan conflicts of old.

At a single stroke, we learn that the Earth is not a newcomer to space exploration – indeed, having fought battles against the Romulans in the past, old resentments still linger. These attitudes are articulated by Lt. Stiles (Paul Comi) who directs his bitterness towards Mr Spock (due to the shared Vulcan/Romulan heritage).

Whilst Stiles is a character type we’ve seen before – a loose cannon aboard the Enterprise – his racist and xenophobic attacks on Mr Spock still have an impact. Not only because by now the viewer has come to embrace Spock as a key member of the crew, but also because they help to shatter the commonly held view that the Star Trek universe is one where such attitudes no longer exist.

As has been observed in the past, Balance of Terror plays out like a WW2 submarine movie. Two equally matched captains – Kirk and the unnamed Romulan Commander (played by Mark Lenard) – engage in a tense game of cat and mouse.

Lenard is, of course, excellent and it’s easy to see why the series was keen to have him back as soon as possible. Spock might describe the Romulans as warlike, cruel and treacherous but that’s a far from accurate portrait of Lenard’s Commander, who is honourable, poetic and world weary.

Unlike his junior officer Decius (Lawrence Montaigne), the Commander has no stomach for war – suggesting that unlike his superior Decius has yet to encounter a real battle. 

The Romulan Commander may not wish to fight, but he is honour bound to do so. That doesn’t mean that he has to relish the prospect though (unlike Decius). “No need to tell you what happens when we reach home with proof of the Earthmen’s weakness. And we will have proof. The Earth commander will follow. He must. When he attacks, we will destroy him. Our gift to the homeland, another war.”

It’s plain that this “gift” is something which will bring only death and destruction, not the glory that Decius seeks.

Had Star Trek gone down the more obvious route, portraying the Romulans as the bloodthirsty types Spock believes they are, then Balance of Terror would still have been a fine episode. But Mark Lenard’s multi-layered performance raises the story up several notches. One of the best – if not the best – Star Trek episodes.